Pneumatic switch



June 1967 R. P. JOHNSTON ETAL 3,328,543

PNEUMATIC SWITCH Filed Sept. 25, 1963 INVENTORS RICHARD P. JOHNSTON ROBERT R. SCHAFFER FIG. 1

ATTORNEY United States Patent O 3,328,543 PNEUMATIC SWITCH Richard P. Johnston and Robert R. Schaifer, Endicott,

N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York The present invention relates generally to switches and it has reference in particular to fluid or pneumatic switches.

Generally stated, it is an object of this invention to provide an improved fluid pressure operated switch.

More specifically, it is an object of the present invention to provide a switch for rapidly opening and closing an electric circuit in response to fluid pressure pulses from logic devices.

Another object of the invention is to provide for connecting and disconnecting spaced conductors in response to relatively high-speed, low pressure pulses such as from fluid logic.

Yet another object of this invention is to provide for using fluid pressure pulses from fluid logic to cause a highsurface tension conducting fluid contained between two conductors to bridge the conductors in timed relation with the pulses.

Still another object of the invention is to provide for using a pair of spaced-apart perforated conductors with a normally nonbridging globule of mercury or the like therebetween, and for subjecting the globule to a pulse of fluid pressure through openings in at least one of the electrodes to cause the globule to contact the other electrode.

Still another object of the invention is to provide for containing a globule of mercury in a cavity between two perforated electrodes with the cavity having a reduced section adjacent one electrode, and for passing pulses of air through the other electrode to drive a portion of the mercury into the reduced section and contact said one electrode.

Yet another object of the invention is to provide an electric switch in which a globule of mercury disposed in a cavity between two perforated electrodes is acted upon by fluid pressure pulses to force a portion of the globule into a reduced section portion of the cavity so as to simultaneously contact both electrodes.

It is also another object of the invention to provide for subjecting a globule of mercury in a cavity between a pair of spaced electrodes to fluid pressure pulses and through openings in one of the electrodes for causing the globule to enter a reduced section portion of a cavity adjacent the other electrode, thereby bridging between the electrodes.

In a preferred embodiment of the invention a fluid pressure pulse operated electric switch suitable for producing a substantially square electrical output wave from pulses such as produced by fluid pressure logic devices is provided by securing a pair of spaced-apart tungsten electrodes in a body of insulating material having a cavity located between the electrodes bounded by the one electrode on one side and having on the other side a reduced or constricted exit channel connecting with the other electrode. The electrodes each have a plurality of fine openings providing entrance and exit passages to and from the cavity. A globule or body of mercury is positioned within the cavity and is subjected to fluid pressure pulses through the holes of the one electrode from an adjoining cavity of suflicient value to overcome the surface tension of the mercury and cause a portion of the globule to distort from the normal contour and enter the reduced exit channel and contact the other electrode so as to bridge ice .. between the electrodes during the pressure pulses. By

connecting the electrodes in circuit with a source of electrical energy, substantially square wave output electrical pulses are obtained.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.

In the drawing:

FIG. 1 is a plan view in enlarged form of a fluid pressure switch embodying the invention in one of its forms.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1.

Referring to FIGS. 1 and 2 of the drawing, the numeral 10 designates generally a body or plate of plastic such as a photopolymer or the like from which the fluid pressure switch of the invention is formed by providing suitable cavities therein by a machining or by an etching process, using a mask with ultraviolet light and removing the masked areas by washing in a sodium hydroxide solution in a manner well known in the art. The body 10 may be secured to a metal or plastic backing plate 12. Entrance and exit cavities 14 and 16 are formed in the body 10 having inlet or entrance and exit or exhaust ports 18 and 20 which are connected to the cavities 14 and 16, respectively, by passages 22 and 24. Intermediate the entrance and exit cavities 14 and 16 is provided a switch cavity 26 having a relatively large opening 28 into the entrance cavity 14, and being connected to the exhaust cavity 16 by means of a reduced cross section or constricted exit channel 30.

Spaced-apart electrodes 32 and 34 are positioned on opposite sides of the switching cavity 26 being for example secured in grooves 36 and 38 formed transversely of the plate 10. Electrodes 32 and 34 are each flat bars of tungsten or other suitable metal not wetted by mercury, and are perforated with a plurality of relatively fine holes or openings 40 in alignrnent with the entrance and exit openings of the switching cavity 26 so as to permit the passage of fluid pressure pulses. A globule of mercury 41 is placed in the switching cavity 26 substantially filling the cavity but not the constricted exit channel 30. A cover plate 42 is secured to the body It by means of screws. 44 to enclose the cavities 14, 1'6 and 216. The electrodes 36 and 38 may be recessed in grooves 46 and 48 in the cover and cemented if necessary so as to provide a substantial seal between the cavities except for the openings 40 in the electrodes.

By making the entrance channel 22 relatively long and narrow, a low pass filter may be provided which effectively removes the usual transient spikes or higher harmonies in the fluid pressure waveform. Assuming that the large cavity 14 contributes to the spring rate, and the small channel 22 contributes to the mass flow, then where f is the resonant frequency of the cavity;

V is the speed of sound;

c, d are the length and width of the large cavity; e is the depth;

1 is the channel length; and

w is the channel width.

For a typical example:

d=.625 inch c=1 inch l=.75 inch w=.020 inch =437 cycles per second.

With an input frequency on the order of 200 cycles per second, a filter of substantially these dimensions provides for passing both the fundamental together with the third and a large percentage of the fifth harmonic but substantially attenuates any higher harmonics.

By providing a reduced or constricted exit channel 30 for the switching cavity 26, a pressure force can be determined at the aperture which is not suflicient to rupture the globule, but will cause the mercury to displace into the channel by overcoming the surface tension of the mercury, since the air or fluid pressure will be transferred through the electrode 32 to the body of the mercury. Under these conditions the switch will be selfrestoring as the surface tension of the mercury causes the globule to withdraw into the cavity 26 as soon as the fluid pressure pulse is over. It may be assumed that the surface tension of the mercury is uniformly distributed and is tangent to the sides of the aperture. The surface tension force may then be equated with the hydrostatic pressure required to overcome the surface tension force, and force a portion of the mercury into the restricted aperture. Accordingly:

then

Ap aXb For a width of apertures,

a=.030 inch, and a depth of apertures, b=.040 inch and the length of the aperture, 1:.020 inch, and a value of F for mercury, 'y=2.78 x per inch.

The following results:

=.325 pound per sqare inch.

Since it has been found by experience that a force of up to four times the threshold pressure will not result in breaking up the globule of mercury, a fluid pressure switch embodying the features of the invention may be operated satisfactory within the range of two to four times the threshold pressure, and with a drop or globule of mercury on the order of three ten thousandths of a cubic inch such a switch has been satisfactorily operated to switch a load of 100 ma. at ten volts at pressures on the order of .65 pound per square inch with a pulse frequency of 200 cycles per second using about eight holes or openings 40 on the order of seven thousandths of an inch each.

Thus when the fluid pressure pulses are applied to the inlet port 18, they are transmitted through the inlet channel 22, where transient spikes, etc. are removed, to the inlet cavity 14 whence they are applied to the globule of mercury in the switching cavity 26 through the opening 40 in the electrode 32. Each time a fluid pulse strikes the globule of mercury it is deformed slightly and a portion thereof is forced into the exit channel 30 to contact the electrode 34 without rupturing the globule, while a portion of the globule remains in contact with electrode 32, thereby bridging between the electrode 32 and 34 so as to provide for controlling an electric circuit to produce substantially square electrical outputwaves. As shown, the switch is provided with an inlet port 18 and an exhaust port 20. When used with a typical fluid pressure logic device, the exhaust port 20 may not be necessary since the inlet or entrance port 18 is selectively connected to a source of fluid pressure and to atmosphere when used with most logic switch devices. While the cross-sectional dimensions of the exit channel 30 determine the operating pressure, the length of the channel affects the distance the mercury has to travel to make contact, and hence affects the delay in the closing of the circuit after the fluid pulse occurs.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A pulse responsive fluid pressure switch comprising (a) a block of insulating material 'having a pair of cavities therein including a major cavity having a minor cavity connected therewith with a principal portion adjacent the major cavity and a constricted portion remote from the major cavity,

(b) a first electrode non-wettable by mercury having a portion with a plurality of perforations on the order of several thousandths of an inch providing a connection between the cavities,

(c) a second electrode non-wettable by mercury having a plurality of perforations on the order of several thousandths of an inch providing an exit from the constricted portion on the end remote from the principal portion of the minor cavity,

(d) a globule of mercury in contact with only the first electrode substantially filling principal portions of the minor cavity and (e) means connected to said major cavity for applying fluid pressure pulses to said major cavity to cause a portion of the globule to enter said constricted portion and bridge both electrodes.

2. In a pulse responsive fluid pressure electric switch,

(a) a body member of insulating material having a pair of connected cavities including a major cavity and a minor cavity,

(b) means defining an exit channel from the minor cavity having a greatly reduced cross section on the order of .0012 square inch,

(0) a first switch electrode non-wettable by mercury positioned between said cavities and having a plurality of relatively small openings each on the order of 4 the area of the exit channel for admitting fluid pressure pulses to said minor cavity,

(d) a second switch electrode non-wettable by mercury positioned across said exit channel and having a plurality of relatively small perforations each on the order of the area of that of the exit channel defining the exit from said channel,

(e) an isolated globule of mercury normally in contact only with said first switch electrode substantially filling only said minor cavity and (f) means connected to said major cavity for applying fluid pressure pulses to said major cavity for forcing a portion of said globule to enter the exit channel and bridge between the electrodes.

3. In a fluid pressure switch device,

(a) a body of insulating material having connected major and minor depressions therein,

(in) a cover of insulating material for said body to enclose said depressions and provide connected major and minor cavities,

(c) means defining a constricted exit channel from the minor cavity,

((1) a first switch electrode non-wettable by mercury separating the cavities and having a plurality of relatively fine openings on the order of .007 in diameter therein connecting the cavities,

(e) a second switch electrode non-wettable by mercury intersecting the exit channel and having a plurality of relatively fine openings on the order of .007 in diameter therein providing exit ports from the exit channel,

(f) an isolated globule of mercury normally in contact with the first switch electrode and not with the second switch electrode substantially filling only the minor cavity and (g) means connected to said major cavity for applying fluid pressure pulses to the major cavity to force a portion of the globule into the exit channel in contact with said second electrode while maintaining contact with the first electrode.

4. In a fluid pressure switch,

(a) means defining connected major and minor cavities in a body of insulating material,

(b) a first switch electrode non-wettable by mercury positioned between said cavities and having a plurality of relatively small openings on the order of .007 in diameter defining the connection between the cavities,

(c) means defining a constricted exit channel on the 5 order of .03 inch by .04 inch for the minor cavity,

(d) a second switch electrode non-wettable by mercury positioned across said exit channel and having a plurality of relatively small openings providing an exit from said channel,

(e) a globule of mercury normally in contact with said first switch electrode and out of contact with said second switch electrode substantially filling said minor cavity and (f) means connected to the switch body including a relatively long narrow inlet opening to said major cavity providing a low pass filter for applying fiuid pressure pulses to said globule through the openings in said one electrode for forcing a portion of the globule into the constricted exit opening to contact said second electrode whereby said globule bridges between the electrodes during each pulse.

References Cited UNITED STATES PATENTS 1,194,324 8/1916 Williams 200-152 1,927,893 9/1933 Kesselring 200-152 BERNARD A. GILHEANY, Primary Examiner. G. MAIER, H. BROOME, Assistant Examiners. 

1. A PULSE RESPONSIVE FLUID PRESSURE SWITCH COMPRISING (A) A BLOCK OF INSULATING MATERIAL HAVING A PAIR OF CAVITIES THEREIN INCLUDING A MAJOR CAVITY HAVING A MINOR CAVITY CONNECTED THEREWITH WITH A PRINCIPAL PORTION ADJACENT THE MAJOR CAVITY AND A CONSTRICTED PORTION REMOTE FROM THE MAJOR CAVITY, (B) A FIRST ELECTRODE NON-WETTABLE BY MERCURY HAVING A PORTION WITH A PLURALITY OF PERFORATIONS ON THE ORDER OF SEVERAL THOUSANDTHS OF AN INCH PROVIDING A CONNECTION BETWEEN THE CAVITIES, (C) A SECOND ELECTRODE NON-WETTABLE BY MERCURY HAVING A PLURALITY OF PERFORATIONS ON THE ORDER OF SEVERAL THOUSANDTHS OF AN INCH PROVIDING AN EXIT FROM THE CONSTRICTED PORTION ON THE END REMOTE FROM THE PRINCIPAL PORTION OF THE MINOR CAVITY, (D) A GLOBULE OF MERCURY IN CONTACT WITH ONLY THE FIRST ELECTRODE SUBSTANTIALLY FILLING PRINCIPAL PORTIONS OF THE MINOR CAVITY AND (E) MEANS CONNECTED TO SAID MAJOR CAVITY FOR APPLYING FLUID PRESSURE PULSES TO SAID MAJOR CAVITY TO CAUSE A PORTION OF THE GLOBULE TO ENTER SAID CONSTRICTED PORTION AND BRIDGE BOTH ELECTRODES. 